In the process of semiconductor device production, semiconductor chips are produced by forming a circuit such as IC, LSI or the like in a plurality of regions sectioned by a plurality of streets on the front surface of a substantially disk-like semiconductor wafer and dicing along the streets. In order to improve the heat radiation of the thus manufactured semiconductor chip, it is desired that the semiconductor chip be made as thin as possible. Also, to enable the downsizing of a portable telephone, smart card or personal computer that uses a large number of semiconductor chips, it is desired that the semiconductor chip be made as thin as possible. To this end, before the semiconductor wafer is divided into individual semiconductor chips by dicing, the back surface of the semiconductor wafer is processed to a thickness of about 50 μm by grinding.
When the back surface of the semiconductor wafer is ground to reduce its thickness, both sides of the semiconductor wafer are warped toward the front surface side. For example, when the back surface of a semiconductor wafer having a diameter of 200 mm is ground to a thickness of 50 μm, both sides of the semiconductor wafer are warped toward the front surface side by about 60 mm. It has been found that this warping of the semiconductor wafer is caused by a coating layer formed by applying a polyimide resin having excellent heat resistance, electric insulating properties and mechanical strength to the front surface of the semiconductor wafer and baking it in order to protect circuits formed on the front surface of the semiconductor wafer, or another coating layer such as a metal layer, insulating layer or the like. That is, a stress for pulling toward the center direction is generated in the coating layer formed on the front surface of the semiconductor wafer. Therefore, when the back surface of the semiconductor wafer is processed to a thinness of about 50 μm thick by grinding, the semiconductor wafer is warped as described above because its stiffness does not withstand the above stress. When the semiconductor wafer is thus warped, it is difficult to smoothly carry out dicing which is a subsequent step.
It is a principal technical subject of the present invention that has been made in view of the above fact to provide a method of processing a semiconductor wafer, which can inhibit the semiconductor wafer from being warped even when its back surface is ground to be processed thin.